For years, an ongoing story line on How I Met Your Mother was about Lily (Alyson Hannigan) hiding her shopping addiction and credit card debt from her husband, Marshall (Jason Segel). She managed to keep her fast-growing stockpile of cute dresses and shoes a secret—until they applied for a mortgage. Suddenly, the gig was up. Because Lily had completely destroyed their credit rating, the couple was forced to live in the only New York City neighborhood they could afford, which was the fictional “Dowisetrepla.” That turned out to be shorthand for downwind of the sewage treatment plant.

That story line is likely to resonate with a surprising number of women—and men, too. A survey of more than 23,000 people by SELF and Today.com found that 46 percent lied about money matters to a significant other at some point—although only 28 percent said a partner had lied to them. One could argue that stretching the truth about one’s spending habits is a harmless quirk of coupled life, as natural as keeping mum about the cute guy at the gym who stops by your treadmill to chat. After all, should you really have to explain to your husband why your new designer heels are worth the stratospheric price? And does neglecting to mention your latest purchase to your spouse truly count as cheating or dishonesty?

Many experts would say yes. “Whatever the amount of money in question, telling lies or keeping secrets threatens your relationship’s stability,” says Amanda Clayman, a psychotherapist in New York City who specializes in financial wellness. “Money is connected to our sense of security. Most people experience any breach of that security as a profound breach of trust.” That’s easy enough to agree with: In the SELF-Today.com survey, 70 percent of women say being honest about money is as important to the health of a relationship as being monogamous. Yet despite those numbers, 32 percent of women admitted that they’d hidden purchases or receipts from a partner; 26 percent said they’d pretended a new purchase wasn’t actually new; and 25 percent had told a spouse they’d bought something on sale when in fact they’d paid full price.

Caroline Parker (not her real name), 26, cops to doing all of those things. An artist in New York City, she says her husband is supporting both of them at the moment. “He’s the steady earner—what I make is the icing on the cake,” she says. “But I haven’t made much lately.” A while ago, Caroline desperately wanted a new bag. “I kept visiting one particular purse over and over, even though I knew I couldn’t afford it. But I couldn’t let it go. So I bought it with the money I’m supposed to use for household stuff. I don’t know how I thought I could hide it—you can’t wear a bag underneath your shirt! I ended up keeping it under the bed for a week. That’s like a month in purse time! When I finally put it on my shoulder and walked downstairs, my husband said, ‘Nice bag!’ and I practically screamed, ‘I got it on triple clearance! They pretty much gave it to me when I walked in the door!'” Except, of course, they hadn’t.

It’s not only handbags women are hiding. It’s haircuts and highlights and all the things we do to keep up appearances in the world. “Men have no idea how much it costs a woman to look good!” Caroline observed. “My husband thinks Botox costs half of what it actually does because I pay the rest in cash,” one interviewee said. Other women fessed up to concealing spontaneous Internet purchases (“I try to rush home to hide the boxes from Net-A-Porter,” one said) or what they buy for their children (“I am flat-out lying to my husband about how much I spent on goody bags for our 5-year-old’s birthday party,” another admitted).

What’s the big deal about a goody bag or two? “If you’re thinking, I can’t tell him this because he’ll be mad or he won’t understand, you’re probably avoiding dealing with issues in your relationship, like who holds the power,” says Marilyn Wechter, a psychotherapist and wealth counselor in St. Louis. “Because often, money is power. For instance, maybe your spouse makes all the spending rules and lying is the only way you feel you can regain control.” Or, maybe you’re the major breadwinner in the household; because you’re earning most of the cash, you feel entitled to splurge without telling your partner. “Bringing it up is going to feel uncomfortable,” Wechter says, “but these feelings are worth thinking and talking about.”

Stay silent, and little lies and omissions can lead to much bigger emotional rifts. Emily Rossi (not her real name) discovered that the hard way. The 35-year-old and her husband were living beyond their means, struggling to keep up with bills and mortgage payments. Then, one day, she went into his bag to grab her sunglasses. “I found a checkbook for an account I’d never seen,” Emily says. “Tucked into it was a list of collectibles he’d been buying on the sly. He’d spent tens of thousands of dollars, and we were broke!”

Emily confronted her husband, who claimed he intended to sell the stuff for a profit on eBay—he just hadn’t gotten around to it yet. He said he’d hidden his not-so-small venture because he knew she wouldn’t approve. Suddenly, Emily saw their financial life—and her spouse—through new eyes. “I thought our debt was because of the house. Now I realized much of it was because of his secret spending,” she says. Emily might have discovered this earlier, but she hadn’t looked at a bill or bank statement in months. Instead, she left that to her husband. “I was so freaked out by our finances, I didn’t want to deal,” Emily says.

Her willful oblivion played a role in the deception, too, Wechter says. “When you’re on the receiving end of a financial betrayal, you have to ask yourself, What was my part in this?” she explains. If you don’t keep track of your finances—either because you’re afraid of what you’ll find out or because you have a fantasy that a man will take care of you—you’re giving up responsibility for your own life, Wechter notes.

In the end, Emily wasn’t able to get beyond her husband’s patent dishonesty. Although the two tried couples counseling, she still felt furious. Shortly afterward, they divorced. In the SELF-Today survey, 13 percent of respondents who’d experienced financial betrayal said they ultimately broke up or, if they were married, divorced. Another 50 percent said it was tough to get the relationship back on solid footing. “Secrets create distance, which then starts to feel as if it’s the norm,” says Maggie Baker, Ph.D., a psychologist and author of Crazy About Money. “That’s when the relationship begins to falter.”

When It’s Time for the Money Talk

If discussing money feels awkward, you’re not alone. “Understandably, most people dread discussing their past sexual history with a new partner; talking about money can be as tough,” says Catherine Birndorf, M.D., founding director of the Payne Whitney Women’s Program at NewYork-Presbyterian Hospital in New York City and SELF’s mental health expert. But to pave the way for an honest financial partnership, “it’s ideal to have a talk early on—and definitely before marriage,” she says. “You need to unpack your money baggage, whether it’s lingering college debt or the 20 credit cards in your wallet. A partnership isn’t only about love. It’s about trust. Being honest about money creates the foundation for that trust.”

So sit down and trade answers to the following questions: (1) How did your family handle money? (2) What are your financial goals, values, weaknesses and successes? (3) Are you a spender or saver? (4) Do you have debt? A secret nest egg? (5) What do you value spending money on? The questions may sound daunting, but if you begin your life in a place of openness, you’re likely to continue on that way.

Once you have your mutual money histories down, you need to lay the ground rules for the future. Experts say there are two good strategies for building a healthy financial life together, whether you’re just starting out or you’ve been together for years. The first (and, granted, this one isn’t for everyone): Agree to keep each other in the loop about your day-to-day spending, whether it’s weekly grocery bills or a spur-of-the-moment spring shopping spree. This kind of exhaustive financial accounting typically works best for a couple who is trying to recover from financial infidelity or one who is trying to save for something big, like buying a home. And it helps if both partners enjoy sitting down on a weekly or monthly basis and reviewing how far they’ve gotten toward their goal.

“The key is that you’re checking in with one another because you’re excited about your shared objectives, not because you’re bent on micromanaging each other’s spending,” says April Lane Benson, Ph.D., a psychologist in New York City. If that’s not the case, keeping track of every penny can feel stifling, especially if one person is more gung ho about this approach than the other. “Both of you have to be on the exact same page for this to work,” Benson says. “If one person feels like she’s dealing with the shopping police, it can lead to lying about spending.”

What to Tell—and What to Keep Private

Not so excited about instituting a share-all, no-secrets-whatsoever policy? There’s a second way to foster openness without laying everything on the table. Instead of itemizing your weekly expenditures, you and your partner agree on how much money each of you can spend every month without having to account for it. “People deserve some privacy and autonomy with money, as with other parts of the relationship,” Clayman says. “The key is that you agree on how far that autonomy goes. To reach that kind of agreement, you need to look at your budget together and say, ‘After we cover our main expenses and contribute to our savings accounts, each of us has X amount of money we can spend without having to justify it.’ ” Translation: If both of you keep to the agreed-upon parameters, a “Don’t ask, don’t tell” policy can be A-OK.

The payoff for all this financial frankness goes beyond a more robust bottom line. (Ahem—you may discover that when you’re not seething at your guy, you’re more apt to want to have sex with him!) “I felt worse and worse about hiding my spending from the person I loved,” Caroline says. “When my husband comes home, I don’t want to think, OMG, I’ve got to stash the Zappos boxes! I want to think, Yay! I’m so glad he’s here.”

Why We Lie or Keep Mum

35% say: I lie when my husband and I disagree over what’s worth spending money on.

34% say: I earn part of our money, so I deserve to be able to spend it, no questions asked.

23% say: I pay the bills, so I don’t see a need to clue in my husband.

19% say: My husband gets angry about anything I spend, so I just keep quiet.

17% say: I like splurging on our kids, but my husband disapproves.

What to Say to a “Cheating” Spouse

Picture this: Your husband comes home one day with a surprise—a brand-new, top-of-the-line luxury car. It’s a beauty, but your current car has only 20,000 miles on it. What to do: Wait until you’re not hyperventilating with crazed, heartpounding fury, then ask him to make a date to discuss the issue, Benson says. The point is to clarify your mutual money values and start talking.

A sample convo…

You: “That’s some car, honey!” (An open-ended statement will encourage him to talk.)

Him: “I know! I’ve always wanted a Beemer, and the dealership was having a crazy sale. You’ll love it.”

You: “I’m sure I will, but I thought we were saving for a big vacation this year. I’m open to making changes in our plan, but let’s discuss them first.” (Frame the issue at hand as an “us” problem. That way, he’ll see you as caring, not a killjoy.)

Him: “I knew if I did, you’d put the kibosh on it!”

You: “Well, I might have. But that’s because I worry that more car payments are going to increase our money stress. I think before either of us makes another big purchase, we need to sit down and see how it fits into our budget.” (Explain your feelings without being accusatory.)